Corrosion and alkali-resistant compositions and methods for using the same

ABSTRACT

A corrosion resistant, alkali resistant coating composition is disclosed. The composition comprises a binder comprising a reaction product of an epoxy-containing material and a phosphorus-containing material together with a curing agent. Aminoplasts, especially melamine-based aminoplasts, are particularly suitable curing agents. A source of silicon can optionally be included. The compositions also provide excellent adhesion and can be used with or without a weldable primer. The compositions are applied to and cured on a metal substrate.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/880,942, entitled, “Corrosion and Alkali-ResistantCompositions and Methods For Using The Same”, filed Jun. 30, 2004, whichis a division of U.S. patent application Ser. No. 10/288,774, filed Nov.6, 2002, both of which are herein incorporated by reference in theirentirety.

FIELD OF THE INVENTION

The present invention relates to coatings for metal substrates, and morespecifically, to coatings that offer both corrosion resistance andalkali resistance.

BACKGROUND OF THE INVENTION

It is known to treat various metals with compositions that will promotesuch things as corrosion resistance and adhesion between the metal andother coatings. While use of chromium compounds provides corrosionresistance and adhesion, such compounds are undesirable because of theirtoxicity and problems with their disposal. Many compounds that provideor approach the level of corrosion protection and/or adhesion offered bychromium compounds, however, do not provide adequate alkali resistance,which is also a desirable quality. Alkali resistant pretreatments canmitigate cathodic delamination. Also, in cases where such a compositionis applied on preprimed metal, an alkaline cleaner is often employedafter fabrication prior to further coating. Thus, improved compositionsthat provide good corrosion resistance, adhesion, and alkali resistanceare desired. It is especially desired that such compositions allow forweldability, either when used alone or in conjunction with a weldableprimer.

SUMMARY OF THE INVENTION

The present invention provides a coating comprising a novel resinousbinder/curing agent combination that provides both corrosion and alkaliresistance, while at the same time providing excellent adhesion betweenthe metal substrate and any subsequent coatings. In one embodiment,silicon is used in the composition to provide enhanced corrosionprotection without significantly interfering with weldability. Thecompositions can be used, if desired, with a weldable primer.

Silicon is thought to offer corrosion inhibition by acting as asacrificial anode for the metal being coated. As such, the metal isprotected cathodically from corrosion by the silicon. In addition tothis cathodic protection, the silicon is also thought to act as anoxygen scavenger. As the various coating layers on a substrate age,water and oxygen slowly diffuse so as to come into contact with thesilicon. The silicon reacts with these substances to produce oxides,such as silicon dioxide (SiO₂), which protect against corrosion. Theinventors do not wish to be bound by any mechanisms, however.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a composition comprising a binderand a curing agent. More specifically, the binder is a resinous bindercomprising a reaction product of one or more epoxy-functional materialsand one or more phosphorus-containing materials. The reaction productcan be a β-hydroxy phosphorus ester having reactive functional groups.These functional groups are typically hydroxyl groups, including acidichydroxyls, and/or epoxy groups, depending on the equivalent ratio of thephosphorus-containing material to epoxy-containing material. “Phosphorusester” will be understood as including both phosphate and phosphonateesters.

Suitable epoxy-functional materials for use in preparing the binders ofthe present invention contain at least one epoxy or oxirane group in themolecule, such as monoglycidyl ethers of a monohydric phenol or alcoholor di- or polyglycidyl ethers of polyhydric alcohols. In one embodiment,the epoxy-functional material contains at least two epoxy groups permolecule and has aromatic or cycloaliphatic functionality to improveadhesion to a metal substrate. In some embodiments, the epoxy-functionalmaterials may be relatively more hydrophobic than hydrophilic in nature.In one embodiment, the epoxy-containing material is a polymer having anumber average molecular weight (Mn) of from about 220 to 25,000, suchas 220 to 4500. The Mn can be determined, for example, by multiplyingthe epoxy equivalent weight (epoxy equivalent) by the epoxyfunctionality (number of epoxy groups). Good alkali resistance istypically obtained when the Mn of the epoxy-containing material isgreater than 1000, such as greater than 1500.

Examples of suitable monoglycidyl ethers of a monohydric phenol oralcohol include phenyl glycidyl ether and butyl glycidyl ether. Suitablepolyglycidyl ethers of polyhydric alcohols can be formed by reactingepihalohydrins with polyhydric alcohols, such as dihydric alcohols, inthe presence of an alkali condensation and dehydrohalogenation catalystsuch as sodium hydroxide or potassium hydroxide. Useful epihalohydrinsinclude epibromohydrin, dichlorohydrin and especially epichlorohydrin.

Suitable polyhydric alcohols can be aromatic, aliphatic orcycloaliphatic and include but are not limited to phenols that are atleast dihydric phenols, such as dihydroxybenzenes, for exampleresorcinol, pyrocatechol and hydroquinone;bis(4-hydroxyphenyl)-1,1-isobutane; 4,4-dihydroxybenzophenone;bis(4-hydroxyphenyl)-1,1-ethane; bis(2-hydroxyphenyl)methane;1,5-hydroxynaphthalene; 4-isopropylidene bis(2,6-dibromophenol);1,1,2,2-tetra(p-hydroxy phenyl)-ethane; 1,1,3-tris(p-hydroxyphenyl)-propane; novolac resins; bisphenol F; long-chain bisphenols; and2,2-bis(4-hydroxyphenyl)propane (bisphenol A), which is especiallysuitable. Aliphatic polyhydric alcohols that can be used include but arenot limited to glycols such as ethylene glycol, diethylene glycol,triethylene glycol, 1,2-propylene glycol, 1,4-butylene glycol,2,3-butylene glycol, pentamethylene glycol, polyoxyalkylene glycol;polyols such as sorbitol, glycerol, 1,2,6-hexanetriol, erythritol andtrimethylolpropane; and mixtures thereof. An example of a suitablecycloaliphatic alcohol is cyclohexanedimethanol.

Epoxy-containing polymers useful in the present invention are disclosedin U.S. Pat. Nos. 5,294,265; 5,306,526 and 5,653,823, which are herebyincorporated by reference. Other useful epoxy-containing materialsinclude epoxy-functional acrylic polymers, glycidyl esters of carboxylicacids and mixtures thereof. Suitable commercially availableepoxy-containing polymers are available from Shell Chemical Companyunder the names EPON 836, EPON 828, EPON 1002F and EPON 1004F. EPON 836and EPON 828 are epoxy-functional polyglycidyl ethers of bisphenol Aprepared from bisphenol A and epichlorohydrin. EPON 828 has an Mn ofabout 400 and an epoxy equivalent weight of about 185 to 192. EPON 836has an Mn of about 625 and an epoxy equivalent weight of about 310 to315. EPON 1002F has an Mn of about 1300 and an epoxy equivalent weightof about 650, while EPON 1004F has an Mn of about 1840 and an epoxyequivalent weight of about 920.

As discussed above, the epoxy-containing material is reacted with one ormore phosphorus-containing materials to form an ester, such as anorganophosphate or organophosphonate. Suitable phosphorus-containingmaterials include phosphonic acids, phosphorous acid, phosphoric acidsincluding super- and poly-, and mixtures thereof. Phosphoric acids areparticularly suitable.

Examples of suitable phosphonic acids include those having at least onegroup of the structure:—R—PO—(OH)₂where R is —C—, such as CH₂ or O—CO—(CH₂)₂—. Nonlimiting examples ofsuitable phosphonic acids include 1-hydroxyethylidene-1,1-diphosphonicacid, methylene phosphonic acids, and alpha-aminomethylene phosphonicacids containing at least one group of the structure:

such as (2-hydroxyethyl)aminobis(methylene phosphonic) acid,isopropylaminobis(methylenephosphonic) acid and other aminomethylenephosphonic acids disclosed in U.S. Pat. No. 5,034,556 at column 2, line52 to column 3, line 43, which is hereby incorporated by reference.

Other useful phosphonic acids include alpha-carboxymethylene phosphonicacids containing at least one group of the structure:

Nonlimiting examples of suitable phosphonic acids includebenzylaminobis(methylene phosphonic) acid, cocoaminobis(methylenephosphonic) acid, triethylsilylpropylamino(methylene phosphonic) acidand carboxyethyl phosphonic acid.

The equivalent ratio of the phosphorus-containing material to theepoxy-containing material is within the range of 0.3 to 5.0:1, such as0.5 to 3.5:1. When using phosphorus to epoxy materials in this ratio,typically only hydroxyl groups will be present on the β-hydroxyphosphorus ester reaction product. In certain embodiments of the presentinvention, the phosphorous-containing material comprises a phosphoricacid and the equivalent ratio of the phosphorus-containing material tothe epoxy-containing material is selected so as to result in acomposition comprising unreacted phosphoric acid. In certainembodiments, therefore, the equivalent ratio of thephosphorous-containing material to the epoxy containing material iswithin the range of 1.0 to 5.0:1, such as 1.6 to 5.0:1. In suchembodiments, a considerable amount of unreacted phosphoric acid remainsin the compositions, which can make the present compositions especiallysuitable for use as a nonchrome metal pretreatment composition.Moreover, such embodiments are unlike certain prior art epoxy phosphateester resins that are the product of an epoxy-containing material andphosphorous-containing material wherein the ratio of thephosphorous-containing material to epoxy-containing material is no morethan 0.8:1. In such resins, the formation of free phosphoric acid is tobe avoided. Moreover, in the present invention, the epoxy-containingmaterial and the phosphorus-containing material can be reacted togetherby any suitable method known to those skilled in the art, such as thereverse phosphatization reaction in which the epoxy-containing materialis added to the phosphorus-containing material.

The resinous binder of the present invention also comprises a curingagent having functional groups that are reactive with the functionalgroups of the epoxy/phosphorus reaction product described above. Thecuring agent can be selected from aminoplasts, polyisocyanates,polyacids, organometallic acid-functional materials, polyamines,polyamides and mixtures of these, depending on the functional groupspresent in the reaction product. The selection of the appropriate curingagent(s) is well within the skills of those practicing in the art.

Suitable aminoplasts can be obtained from the condensation reaction offormaldehyde with an amine or amide. Examples include but are notlimited to melamine, urea and benzoguanamine. Although condensationproducts obtained from the reaction of alcohols and formaldehyde withmelamine, urea or benzoguanamine are most common, condensates with otheramines or amides can be used. For example, aldehyde condensates ofglycoluril, which yield a high melting crystalline product useful inpowder coatings, can be used. Formaldehyde is the most commonly usedaldehyde, but other aldehydes such as acetaldehyde, crotonaldehyde, andbenzaldehyde can also be used.

The aminoplast can contain imino and methylol groups. A particularlysuitable aminoplast is a melamine formaldehyde condensate having iminogroups, especially such an aminoplast having at least 40 weight percentimino groups. In certain embodiments, at least a portion of the methylolgroups can be etherified with an alcohol to modify the cure response.Any monohydric alcohol like methanol, ethanol, n-butyl alcohol,isobutanol, and hexanol can be employed for this purpose. Suitableaminoplast resins are commercially available, for example, from CytecIndustries, Inc. in its CYMEL line and from Solutia, Inc. in itsRESIMENE line. Particularly suitable products are CYMEL 385 (especiallyfor water-based compositions), CYMEL 1158 imino-functional melamineformaldehyde condensates, and CYMEL 303.

As noted above, polyisocyanate curing agents can also be used. As usedherein, the term “polyisocyanate” is intended to include blocked (orcapped) polyisocyanates as well as unblocked polyisocyanates. Thepolyisocyanate can be aliphatic, aromatic, or mixtures thereof. Althoughhigher polyisocyanates such as isocyanurates of diisocyanates are oftenused, diisocyanates can be used. Higher polyisocyanates also can be usedin combination with diisocyanates. Isocyanate prepolymers, for examplereaction products of polyisocyanates with polyols, can also be used, ascan mixtures of polyisocyanates.

If the polyisocyanate is blocked or capped, any suitable aliphatic,cycloaliphatic, or aromatic alkyl monoalcohol known to those skilled inthe art can be used as a capping agent for the polyisocyanate. Othersuitable capping agents include oximes and lactams. Other useful curingagents comprise blocked polyisocyanate compounds, such as thetricarbamoyl triazine compounds described in detail in U.S. Pat. No.5,084,541, which is incorporated herein by reference. U.S. Pat. No.4,346,143, column 5, lines 45-62, describes blocked or unblocked di- orpolyisocyanates such as toluene diisocyanate blocked with caprolactamand is also incorporated by reference herein. A toluene diisocyanateblocked with caprolactam is commercially available from BayerCorporation under the trademark DESMODUR BL 1265.

Suitable polyacid curing agents include acid group-containing acrylicpolymers prepared from an ethylenically unsaturated monomer containingat least one carboxylic acid group and at least one ethylenicallyunsaturated monomer that is free from carboxylic acid groups. Such acidfunctional acrylic polymers can have an acid number ranging from 30 to150. Acid functional group-containing polyesters can be used as well.Polyacid curing agents are described in further detail in U.S. Pat. No.4,681,811 at column 6, line 45 to column 9, line 54, which isincorporated herein by reference.

Useful organometallic complexed materials that can be used as curingagents include a stabilized ammonium zirconium carbonate solutioncommercially available from Magnesium Elektron, Inc. as BACOTE 20,stabilized ammonium, zirconium carbonate, and a zinc-based polymercrosslinking agent commercially available from Ultra AdditivesIncorporated as ZINPLEX 15.

Examples of suitable polyamine curing agents include primary orsecondary diamines or polyamines in which the radicals attached to thenitrogen atoms can be saturated or unsaturated, aliphatic, alicyclic,aromatic, aromatic-substituted-aliphatic,aliphatic-substituted-aromatic, and heterocyclic. Suitable aliphatic andalicyclic diamines include 1,2-ethylene diamine, 1,2-propylene diamine,1,8-octane diamine, isophorone diamine, propane-2,2-cyclohexyl amine,and the like; suitable aromatic diamines include phenylene diamines andtoluene diamines, for example o-phenylene diamine and p-tolylenediamine. These and other suitable polyamines are described in detail inU.S. Pat. No. 4,046,729 at column 6, line 61 to column 7, line 26, whichis incorporated herein by reference.

Appropriate mixtures of curing agents may also be used in the invention.

The weight percent of the binder in the present compositions typicallyranges from about 50 to 100 percent, such as 75 to 95 percent, or 80 to90 percent, with weight percent based on the total weight of thecomposition. The weight percent of the curing agent, if used, generallyranges from 5 to 25 weight percent based on the total weight of theresinous binder.

The present compositions comprising the epoxy/phosphorus reactionproduct and curing agent provide excellent corrosion resistance, alkaliresistance and adhesion properties. Significantly, this composition canbe used in conjunction with a weldable primer, without significantlyimpacting weldability. In such embodiments, the weldable primer istypically directly adjacent to a cured layer deposited from the presentcompositions. When used with a weldable primer, the present compositionsare typically deposited so as to form a coating layer that is thickenough to provide corrosion resistance without inhibiting welding;thicknesses much greater than about 1.0 micron can negatively impactwelding such that their use would be undesirable, and thicknesses muchless than 0.1 would not provide suitable corrosion resistance. Athickness of between about 0.2 and 0.8 microns is typically suitable.

Any weldable primer can be used in conjunction with the presentcomposition. A “weldable primer” will be understood as a compositioncomprising one or more electroconductive pigments that provideelectroconductivity to the weldable coating and one or more binders thatadhere the electroconductive pigment to the substrate or anypretreatment coating deposited on the substrate. Commercially availableweldable primers include BONAZINC 3000, BONAZINC 3001, and BONAZINC3005, from PPG Industries, Inc.

The present compositions further comprise a source of silicon. Siliconcan be obtained, for example, in powder form or pieces. For use in thepresent invention, the average particle size of silicon can be 0.2 to 10microns, such as 1 to 5 microns. The size of the silicon particle usedcan be determined based on the desired thickness of the coating layer.Silicon is commercially available in a number of grades, such astechnical grade, high purity and ultra-high purity. High purity siliconis a waste product of wafer production in the electronics industry andis therefore readily available. Suitable commercially available productsinclude SI-1059 from Elkem (average particle size of <10μ; 99.20%silicon) and SI-100 from AEE (average particle size between 1 and 5μ;99.20% silicon). The weight ratio of silicon to binder/curing agent istypically from about 0.01 to 1.0. The weight percent of silicon in thetotal composition is typically from about 1.0 to 30.0. It will beunderstood that silicon is a semiconductive material; a semi-conductivematerial is a substance having two separate bands of “energy equivalent”molecular orbitals that are very close in energy. The lower energy bandis completely filled with “paired” electrons and the higher energy bandis completely empty of electrons. Since the energy gap between the twobands is very small, thermal energy can promote electrons from the lowerfilled band to the higher unfilled band producing band(s) that havesmall numbers of unpaired electrons, which in turn permits theestablishment of a weak electric current. The present compositions aresubstantially free of conductive pigments; a conductive pigment is onethat, on a molecular scale, has a partially filled band of “energyequivalent” molecular orbitals. This partially filled band has many“unpaired” electrons that are able to move freely from atom to atomwithin the conductive pigment matrix. The free flow of electrons withinthe matrix produces an electric current. “Substantially free” means thatthere is <1 weight percent of conductive pigment in the composition,such as <0.5 weight percent or even <0.1 weight percent.

When the present compositions comprise silicon, they can still be usedin conjunction with a weldable primer, as described above. The thicknessof the deposited layer under the weldable primer is typically from about0.01 to 2, such as 0.01 to 0.5.

It has been surprisingly discovered that the present silicon-containingcompositions can also be used without a weldable primer. Thesecompositions, as noted above, are substantially free of conductivepigments. When used without a weldable primer, the presentsilicon-containing compositions are typically applied in a thickness ofabout 2.2 microns or less.

The present coating compositions may contain a diluent added to adjustthe viscosity of the coating composition. For application to asubstrate, the present compositions should typically have a viscosity offrom about 30 to 180 seconds as measured by a No. 4 Ford Cup. If adiluent is used, it should be selected so as not to detrimentally affectthe adhesion of the curable coating composition to a metal substrate.Useful diluents include water (“aqueous based”), organic solvents (whichwould be referred to as either aqueous based or solvent based” dependingon which is the major diluent). Water is preferred in many applications,as the use of aqueous-based forms of the present composition canactually result in increased weldability of the coating layer depositedtherefrom, as compared with its solvent-based counterpart.

When water is included as a diluent, dispersants, thickeners, defoamers,stabilizers, rheology modifiers, and anti-settling agents are typicallyused as well. A suitable rheology modifier is available from Rohm andHaas Company as Rheology Modifier RM-8, Experimental. A suitablestabilizing and dispersing agent is potassium tripolyphosphate (KTPP).

Optimally, the aqueous composition contains an amine. Particularlysuitable amines are hydroxyl-containing amines. The volatile organiccompound content (VOC content) of the aqueous composition will typicallybe less than 2.4, such as less than 1.7, as determined by Method 24,which will be familiar to those skilled in the art.

The diluent of the present invention can also be an organic solvent.Suitable organic solvents include alcohols having up to about 8 carbonatoms, such as ethanol and isopropanol, and alkyl ethers of glycols,such as 1-methoxy-2-propanol, and monoalkyl ethers of ethylene glycol,diethylene glycol and propylene glycol. In a particularly suitableembodiment, the diluent includes a propylene glycol monomethyl ether ora dipropylene glycol monomethyl ether. A suitable propylene glycolmonomethyl ether is available from Dow Chemical Company as DOWANOL PM; asuitable dipropylene glycol monomethyl ether is commercially availableas DOWANOL DPM.

Other suitable organic solvents include ketones such as cyclohexanone(preferred), acetone, methyl ethyl ketone, methyl isobutyl ketone andisophorone; esters and ethers such as 2-ethoxyethyl acetate, andpropylene glycol methyl ether acetates such as PM ACETATE, commerciallyavailable from Dow Chemical Company; and aromatic solvents such astoluene, xylene, and aromatic solvent blends derived from petroleum suchas those available as “Solvesso”.

The solvent-based composition also can contain an amine for stabilitypurposes. The preferred amines are alkyl substituted morpholinecompounds such as N-methyl and N-ethyl morpholine.

The compositions of the invention can further comprise surfactants.Surfactants can be used to improve the wetting of the substrate.Generally, surfactants are present in an amount of less than about 2weight percent on a basis of total weight of the coating composition.Suitable surfactants are commercially available from Air Products andChemicals, Inc. in their SYRFYNOL line, such as SURFYNOL 104 PA.

The coating composition of the present invention can also includecorrosion resistant pigments. Suitable corrosion resistant pigmentsinclude, but are not limited to, zinc phosphate, calcium ion-exchangedsilica, colloidal silica, synthetic amorphous silica, and molybdatessuch as calcium molybdate, zinc molybdate, barium molybdate, strontiummolybdate, and mixtures thereof. Suitable calcium ion-exchanged silicais commercially available from W.R. Grace & Co. as SHIELDEX AC3.Suitable colloidal silica is available from Nissan Chemical Industries,Ltd. as SNOWTEX. Suitable amorphous silica is available from W.R. Grace& Co. as SYLOID. If corrosion resistant pigments are used, they aretypically not used in amounts that will interfere with weldability, thatis, about 20 weight percent or less, based on the total weight of thecomposition.

Other optional ingredients include inorganic lubricants such asmolybdenum disulfide particles that are commercially available fromClimax Molybdenum Marketing Corporation, extender pigments such as ironoxides and iron phosphides, flow control agents, thixotropic agents suchas silica, montmorillonite clay and hydrogenated castor oil,anti-settling agents such as aluminum stearate and polyethylene powder,dehydrating agents that inhibit gas formation such as silica, lime orsodium aluminum silicate, and wetting agents including salts of sulfatedcastor oil derivatives such as those commercially available from CognisCorporation as RILANIT R4.

In one embodiment, the coating compositions are substantially free ofchromium-containing materials, i.e., contain less than about 2 weightpercent of chromium-containing materials (expressed as CrO₃), less thanabout 0.05 weight percent of chromium-containing materials, or about0.00001 weight percent. Examples of chromium-containing materialsinclude chromic acid, chromium trioxide, chromic acid anhydride,dichromate salts such as ammonium dichromate, sodium dichromate,potassium dichromate, and calcium chromate. In another embodiment, thepresent compositions contain no zeolite.

In practice, the coating composition of the present invention will beapplied to a metal substrate and then cured. Appropriate thicknesses forthe present compositions are described above, and can be furtherdetermined by one skilled in the art based on the particular needs ofthe user. The present compositions, when used with a weldable primer,will be cured before application of the primer.

Metal substrates used in the practice of the present invention includeferrous metals, non-ferrous metals and combinations thereof. Suitableferrous metals include iron, steel, and alloys thereof. Nonlimitingexamples of useful steel materials include cold rolled steel, galvanized(zinc coated) steel, electrogalvanized steel, stainless steel, pickledsteel, zinc-iron alloy such as Galvanneal, Galvalume and Galfanzinc-aluminum alloys and combinations thereof. Useful non-ferrous metalsinclude aluminum, zinc, magnesium and alloys thereof. Combinations orcomposites of ferrous and non-ferrous metals can also be used.

At application, the temperature of the coating composition is typicallyfrom about 10° C. to 85° C., such as from about 15° C. to 60° C. Foraqueous-based coating compositions, the pH of the coating composition atapplication generally ranges from about 7.0 to about 12.0, such as about8.0 to about 10.5. Water-soluble or water-dispersible acids and/or basescan be used to adjust pH, if needed.

The present invention is therefore further directed to a process forcoating a metal substrate by applying any of the compositions describedabove to the substrate and curing the coating to form a layer on thesubstrate. The layer is a corrosion resistant layer, an alkali resistantlayer, an adhesive layer and, in some cases, a weldable layer. Thesubstrate, composition and curing temperatures and application methodsare all as described above.

The compositions of the invention can be applied to the surface of ametal substrate by any conventional application technique, such asspraying, immersion or roll coating in a batch or continuous process.Squeegee or wringer rolls can be used to remove excess coating. Afterapplication, the coating is cured to form a cured coating upon the metalsubstrate. Curing can be achieved at peak metal temperatures of greaterthan or equal to 75° C., such as from 75° C. to 200° C. Peak metaltemperatures of from about 100° C. to 150° C. are particularly suitable.Cure times typically range from 2 seconds to 60 seconds, such as ≧10seconds.

As discussed above, the present compositions provide corrosionresistance to the metal substrates to which they are applied. It hasbeen surprisingly discovered that the present compositions also providealkaline resistance to these substrates. Alkaline or alkali resistancerefers to the ability of a compound to resist removal when exposed tostandard automotive cleaners up to a pH of 14, such as greater than a pHof 13. It is believed that the use of an aminoplast curing agent,particularly a melamine-formaldehyde condensate and more particularlysuch a condensate having greater than about 40 weight percent of iminogroups, contribute to alkali resistance. Accordingly, the presentinvention is further directed to a method for improving the alkaliresistance of a pretreatment layer comprising adding an aminoplast tothe composition from which the layer is deposited. A nonchrome alkaliresistant pretreatment having a coating deposited thereon is also withinthe scope of the present invention. Such a combination exhibits lessthan 10 percent, such as 5 percent or less, of coating removal whencleaned with an alkaline cleaner having a pH of 13 or higher. It will beappreciated that such cleaners can attack certain types of pretreatmentlayers, with the result being that the coating deposited on thepretreatment layer is removed. The present compositions allow forexceptional coating retention after alkaline cleaning.

In addition to corrosion resistance and alkali resistance, the presentcompositions have excellent adhesive characteristics; for example, at athickness of 2.2 microns or less, the present compositions haveexcellent adhesive strength as determined by deformation test methodsstandard in the art such as ASTM E643 and ASTM D2794-93. The presentinvention is therefore further directed to a nonchrome pretreatmentlayer deposited on a substrate, wherein the thickness of the layer isless than or equal to 2.2 microns and wherein 10 percent or less, suchas 5 percent or less, of the coating is removed from the substrate whentested according to ASTM E643 or ASTM D2794-93.

EXAMPLES

The following examples are intended to illustrate the invention, andshould not be construed as limiting the invention in any way.

Example 1

To a 4-neck 3-liter round-bottom flask fitted with a reflux condenser, amechanical stirrer and a nitrogen inlet, were charged at ambienttemperature 36.9 grams (0.32 mole) of 85% phosphoric acid and 50 gramsof propylene glycol monomethyl ether (DOWANOL PM) obtained from DowChemical. The mixture was heated with stirring to 99° C. whilemaintaining a nitrogen blanket. A solution comprising 554 grams (0.3mole) of diglycidylether from epichlorohydrin and bisphenol A (EPON1004F obtained from Shell Chemical Company) and 553 grams of DOWANOL PMwas added to the flask from an addition funnel at 99° C. to 100° C. over52 minutes. The reaction mixture was then held at 100° C. for 53 minutesat which time the epoxy equivalent weight was determined to be greaterthan 20,000. Next, 21.6 grams of deionized water were added and thereaction mixture was held at 100° C. to 104° C. for 123 minutes. Thereaction mixture was then cooled to 82° C., and a vacuum was applied;253 grams of distillate were removed. To the reaction mixture was thenadded 57 grams (0.64 moles) of dimethylethanol amine dissolved in 100grams of deionized water over 8 minutes at 82° C. After mixing well,934.5 grams of deionized water (preheated to approximately 70° C.) wereadded to the reaction mixture at 72° C. to 57° C. over 30 minutes. Thereaction mixture was then cooled and poured into a plastic container.The solids of the resin solution were determined to be 31.1%, and theacid number was determined to be 18.1.

Example 2

At ambient temperature, a water-based, alkali resistant coatingcomposition was made by first adding 24.1 grams of an acetylenicsurfactant (SURFYNOL 104DPM obtained from Air Products and Chemicals,Inc); 11.47 grams of a polyurethane rheology modifier (RM-8 obtainedfrom Rohm and Haas); 12.0 grams of a proprietary defoamer (SURFYNOLDF210 obtained from Air Products and Chemicals, Inc.) to 880.0 grams ofthe product of Example 1. After stirring the resultant mixture for 15minutes with a Cowles blade, 72.4 grams of a melamine-formaldehydecondensate (CYMEL 385 obtained from Cytec Industries, Inc.) was addedand the entire mixture was stirred for an additional 10 minutes. Theinitial viscosity was about 72 seconds (#4 Ford Cup), and a grind gaugemeasurement was determined to be greater than 7 (Hegman).

Example 3

At ambient temperature, a water-based, alkali resistant coatingcomposition was made by first adding 78.1 grams of calcium exchangedsilica (SHIELDEX AC3 obtained from Davison Chemical Division of W.R.Grace & Co.) to 77.5 grams of deionized water. The mixture was stirredwith a Cowles blade for 5 minutes. While continuing to stir the mix witha Cowles blade, the following components were added sequentially inone-minute intervals: 20.3 grams of SURFYNOL 104DPM; 740.4 grams of theproduct of Example 1; 12.7 grams of Rheology Modifier RM-8; and 10.1grams of SURFYNOL DF210. After stirring the resultant mixture for 15minutes with a Cowles blade, 60.9 grams of CYMEL 385 was added and theentire mixture was stirred for an additional 10 minutes. The initialviscosity was about 139 seconds (#4 Ford Cup), and a grind gaugemeasurement was determined to be about 4.5 (Hegman).

Example 4

At ambient temperature, a water-based alkali resistant coatingcomposition was made by first adding 97.4 grams of elemental silicon(SI-1059 obtained from Elkem Metals Co.) to 75.8 grams of deionizedwater. The mixture was stirred with a Cowles blade for 5 minutes. Whilecontinuing to stir the mix with a Cowles blade, the following componentswere added sequentially in one-minute intervals: 19.9 grams of SURFYNOL104DPM; 725.0 grams of the product of Example 1; 12.4 grams of RheologyModifier RM-8; and 9.9 grams of SURFYNOL DF210. After stirring theresultant mixture for 15 minutes with a Cowles blade, 59.7 grams ofCYMEL 385 was added and the entire mixture was stirred for an additional10 minutes. The initial viscosity was about 136 seconds (#4 Ford Cup),and a grind gauge measurement was determined to be about 4 (Hegman).

Example 5

At ambient temperature, a water-based alkali resistant coatingcomposition was made by first adding 64.2 grams of elemental siliconSI-1059 to 78.6 grams of deionized water. The mixture was stirred with aCowles blade for 5 minutes. While continuing to stir the mix with aCowles blade, the following components were added sequentially inone-minute intervals: 20.6 grams of SURFYNOL 104DPM; 751.6 grams of theproduct of Example 1; 12.9 grams of Rheology Modifier RM-8; and 10.2grams of SURFYNOL DF210. After stirring the resultant mixture for 15minutes with a Cowles blade, 6.19 grams of CYMEL 385 was added and theentire mixture was stirred for an additional 10 minutes. The initialviscosity was about 127 seconds (#4 Ford Cup), and a grind gaugemeasurement was determined to be about 4 (Hegman).

Example 6

At ambient temperature, a water-based alkali resistant coatingcomposition was made by first adding 133.6 grams of elemental siliconSI-1059 to 72.8 grams of deionized water. The mixture was stirred with aCowles blade for 5 minutes. While continuing to stir the mix with aCowles blade, the following components were added sequentially inone-minute intervals: 19.1 grams of SURFYNOL 104DPM; 695.9 grams of theproduct of Example 1; 11.9 grams of Rheology Modifier RM-8; and 9.5grams of SURFYNOL DF210. After stirring the resultant mixture for 15minutes with a Cowles blade, 57.3 grams of CYMEL 385 was added and theentire mixture was stirred for an additional 10 minutes. The initialviscosity was about 145 seconds (#4 Ford Cup), and a grind gaugemeasurement was determined to be about 4 (Hegman).

Example 7

At ambient temperature, a water-based alkali resistant coatingcomposition was made by first adding 189.5 grams of elemental siliconSI-1059 to 152.1 grams of deionized water. The mixture was stirred witha Cowles blade for 5 minutes. While continuing to stir the mix with aCowles blade, the following components were added sequentially inone-minute intervals: 15.8 grams of SURFYNOL 104DPM; 577.3 grams of theproduct of Example 1; 9.9 grams of Rheology Modifier RM-8; and 7.9 gramsof SURFYNOL DF210. After stirring the resultant mixture for 15 minuteswith a Cowles blade, 47.5 grams of CYMEL 385 was added and the entiremixture was stirred for an additional 10 minutes. The initial viscositywas about 99 seconds (#4 Ford Cup), and a grind gauge measurement wasdetermined to be about 4 (Hegman).

Example 8

To a 4-neck 3-liter round-bottom flask fitted with a reflux condenser, amechanical stirrer and a nitrogen inlet, were charged at ambienttemperature 113.56 grams (0.985 mole) of 85 percent phosphoric acid and58.82 grams of propylene glycol monomethyl ether (DOWANOL PM) obtainedfrom Dow Chemical plus 10.92 grams of Rhodamine B/DEN-438 adduct. Themixture was heated with stirring to 90° C. while maintaining a nitrogenblanket. A solution comprising 347.19 grams (0.923 mole) ofdiglycidylether from epichlorohydrin and bisphenol A (EPON 880 obtainedfrom Shell Chemical Company) and 115.98 grams of DOWANOL PM was added tothe flask from an addition funnel at 90° C. to 100° C. over 60 minutes.The reaction mixture was then held at 90° C. for 60 minutes at whichtime the epoxy equivalent weight was determined to be greater than20,000. Next, 62.24 grams of deionized water were added and the reactionmixture was held at 90° C. for 240 minutes. The reaction mixture wasthen cooled to 70° C. To the reaction mixture was added 7.77 grams ofammonium bifluoride (0.136 mole) diluted with 50 g of deionized water.To the reaction mixture at 50° C. was then added 170.2 grams (2.00moles) of ammonia at 20 percent in deionized water dissolved with 54.37grams of deionized water over 20 minutes (added to the flask from anaddition funnel) leading to an exotherm at 60° C. After mixing well over30 minutes, the reaction mixture was then cooled at 35° C. and 86.61grams of CYMEL 303 (melamine formaldehyde condensate from CYTECIndustries, Inc.) was added to the mixture and the entire mixture wasstirred for an additional 30 minutes, then poured into a plasticcontainer. The solids of the resin solution were determined to be at 53percent and the pH for a 5 percent solution in deionized water was inthe range of 7.0 to 7.5.

Example 9 Panel Preparation

Two-sided 60G Electrogalvanized steel (EG) panels were obtained from USXCorporation and Sollac Steel. Each panel was 15.3 centimeters (cm) wideand 38.1 cm long. The steel panels were subjected to an alkalinecleaning process by spray in a 0.85 percent by weight bath of PARCO 338(P338 from Henkel, Inc.) at a temperature of 65° C. for 10 seconds. Thepanels were removed from the alkaline cleaning bath, rinsed with roomtemperature deionized water (about 20° C.) for 5 seconds and dried withwarm air (about 40° C.).

Adhesion and Corrosion Testing of Present Compositions as a PretreatmentLayer

After cleaning, the steel panels were coated with either a 5 percentsolids deionized water solution of Example 2 or Example 8. The 5 percentsolids solutions of Examples 2 and 8 were applied via Roll Coatapplication (40 psi; 210 rpm) and baked for ˜15 seconds until a peakmetal temperature of 100° C. was achieved. Pretreatment controlsincluded a commercial chromium pretreatment B4513 (available fromHenkel) and a commercial organic pretreatment NUPAL 456BZR (aphosphatized epoxy product from PPG Industries, Inc.). All of the panelswere subsequently coated with a commercially available Weldable Primer,BZ3000 (PPG Industries, Inc.) at 3 to 3.5 microns.

Flat panels prepared as described above were compared in standardadhesion (MEK rubs) and corrosion testing according to Industry StandardProcedure GM 9511P for 20 cycles. Results are shown in TABLE 1. TABLE 1APG TESTING PANELS SUBSTRATE Pretreatment “MEK % Red Rust TESTED‘Coating weight’ Rubs” (Degree of White Stain)¹ USS EG B4513 chrome 50+20-30% ‘30 mg Cr/m²’ (Light) USS EG Nupal 456BZR 50+ 20-30% ‘80-100mg/m²’ (Light) USS EG Example 2 50+ 25-35% ‘80-100 mg/m²’ (Light) USS EGExample 8 50+ 20-30% ‘80-100 mg/m²’ (Light) Sollac EG B4513 chrome 50+20-30% ‘30 mg Cr/m²’ (Light) Sollac EG Nupal 456BZR 50+ 20-30% ‘80-100mg/m²’ (Light) Sollac EG Example 2 50+ 25-35% ‘80-100 mg/m²’ (Light)Sollac EG Example 8 50+ 20-30% ‘80-100 mg/m²’ (Light)¹Values based on the average of two or more test pieces.

As seen in Table 1, the compositions of the present invention hadadhesion and corrosion resistance comparable to that of a commerciallyavailable chrome-containing pretreatment.

To simulate the performance of the pretreatments after forming andcleaning, the four pretreatments as described above (on both substrates)were formed into 35 millimeters (mm) cups with an ErichsenBandprüfmaschine No. 142 from 85 mm disks (draw speed=10). The cups werethen exposed to a pH=13.1 alkaline solution (CHEMKLEEN 190 availablefrom PPG Industries, Inc.). Resistance of the pretreatment to thealkaline solution is determined by the amount of BZ3000 removed. Resultsare shown in Table 2. TABLE 2 Amount of BZ3000 SUBSTRATE PretreatmentRemoved from cup after TESTED ‘Coating weight’ pH 13 alkaline cleaning¹USS EG B4513 chrome 0-5% ‘30 mg Cr/m²’ USS EG Nupal 456BZR  0-10%‘80-100 mg/m²’ USS EG Example 2 0-5% ‘80-100 mg/m²’ USS EG Example 80-5% ‘80-100 mg/m²’ Sollac EG B4513 chrome 0-5% ‘30 mg Cr/m²’ Sollac EGNupal 456BZR 20-30% ‘80-100 mg/m²’ Sollac EG Example 2 0-5% ‘80-100mg/m²’ Sollac EG Example 8 0-5% ‘80-100 mg/m²’¹Values based on the average of two or more test pieces.

Adhesion and Corrosion Testing of Present Compositions as a WeldablePrimer

After cleaning, the steel panels were coated directly (no pretreatment)with the composition of Examples 3-7 using wire drawbars and baked for40 seconds until a peak metal temperature of 154° C. was achieved. Thecorresponding dried film thickness (“DFT”) values for each coating arereported in Table 3. In all cases panels were allowed to air cool toambient temperatures.

Erichsen Ball Punch Deformation Testing (ASTM E643) and 160 PoundResistance of Organic Coatings to the Effects of Rapid Deformation (ASTMD2794-93) was conducted. USS EG panels were cleaned with an alkalinecleaner and coated with the compositions of Examples 3-7. The sampleswere sprayed on the panels for five minutes at 18-20 psi. USS EG panelscoated with Examples 3-7 were also tested in GM P9511P corrosion testingfor 20 cycles. Panels coated with the BZ3000 weldable primer withoutpretreatment and BZ3000 with the B1415A chromium pretreatment (availablefrom Henkel) were also tested. Relative ratings according to the amountof coating removed in the adhesion tests after alkaline cleaning(CHEMKLEEN 490MX available from PPG; pH=12.5; 120° F.; 5 min.) and ofthe percentage of red rust that formed over the entire tested surface ofthe panel, as well as the degree of white stain, are shown in Table 3.TABLE 3 Erichsen 160 lb bump Impact Amount of Amount of Coating CoatingAPG Pretreatment Removed Removed TESTING (PMT Cure) after after % RedRust Variable ‘Dry Film alkaline alkaline (Degree of Tested Thickness’cleaning¹ cleaning¹ White Stain)¹ BZ3000 No pretreatment 100%  100% 40-50% (490F PMT) (Light) 3.5 microns DFT BZ3000/Cr B1415A Chrome 5-10%5-10% 20-30% (490F PMT) (Light) 3.5 microns DFT Example 3 Nopretreatment 5-10% 5-10% <5% (310F PMT) (Light) 2.0 microns DFT Example4 No pretreatment 5-10% 5-10% <5% (310F PMT) (Light) 2.0 microns DFTExample 4 No pretreatment 0% 0% 20-30% (310F PMT) (Light) 1.0 micronsDFT Example 5 No pretreatment 0% 0% <5% (310F PMT) (Light) 2.2 micronsDFT Example 6 No pretreatment 5-10% 5-10% <5% (310F PMT) (Light) 2.0microns DFT Example 7 No pretreatment 5-10% 5-10% <5% (310F PMT) (Light)1.9 microns DFT¹Values based on the average of two or more test pieces.

Weld Testing

The coating compositions of the present invention were tested for spotweldability by coating two steel sheets on both sides with compositionsof the present invention. Efficiency of welding for each variable wasdetermined in accordance with test procedure FLTM BA 13-1 (FordLaboratory Test Method). The test determines the actual life of the 5.5mm (F16) electrode welding tips. Welds are done in 100 weld increments.The first 90 welds are done at 0.1 kA below expulsion. Then ten couponsare welded and the nugget size of each weld is measured. The testcontinues until the average nugget diameter of a 10 coupon set is lessthan 4√{square root over ( )}t, where t is the thickness of one coupon.Results are shown in Table 4. TABLE 4 Pretreatment Number of Weldsbefore Variable (PMT Cure) Average nugget diameter of a 10 Tested ‘DryFilm Thickness’ coupon set is less than 4{square root over (t)}BZ3000/Cr Chrome pretreat 500 490F PMT 3.5 microns DFT Example 3 Nopretreatment 100 310F PMT 2.0 microns DFT Example 4 No pretreatment 500310F PMT 2.0 microns DFT Example 4 No pretreatment 900 310F PMT 1.0microns DFT Example 5 No pretreatment 100 310F PMT 2.0 microns DFTExample 6 No pretreatment 300 310F PMT 2.0 microns DFT Example 7 Nopretreatment 200 310F PMT 2.3 microns DFT¹The welding data included in Table 4 was evaluated using a model 150 APresistance spot welder from Lors Corporation of Union, New Jersey,equipped with a Model 108B welding controller from Interlock Industries,Inc. and Lors Corporation.# The welding current in kilo amperes (kA) was measured using a modelMM-315A Weld Checker from Unitek Miyachi Corporation of Monrovia,California. MB 25Z copper welding tips from the Wheaton Company, Inc. ofWarminster, Pennsylvania with a starting face diameter of 3/16 inch wereused.

The data reported in Tables 3 and 4 above shows that the coatingcompositions of the present invention compare very favorably with thecommercial BZ3000 control. In addition to the increased corrosionresistance and comparable weldability, the compositions of the presentinvention can be applied at lower film thickness without pretreatmentand cured at lower temperatures than commercially available coatings,which typically cure at temperatures of greater than 220° C.

Whereas particular embodiments of this invention have been describedabove for purposes of illustration, it will be evident to those skilledin the art that numerous variations of the details of the presentinvention may be made without departing from the invention as defined inthe appended claims.

1. A composition substantially free from conductive pigments comprising:a) the reaction product of one or more epoxy-containing materials andone or more phosphorus-containing materials comprising a phosphoricacid; and b) a curing agent, wherein the equivalent ratio of thephosphorous-containing material to epoxy-containing material is withinthe range of 1.0 to 5.0:1.
 2. The composition of claim 1, wherein theepoxy-containing material is a polyglycidyl ether of a polyhydricphenol.
 3. The composition of claim 2, wherein the polyhydric phenol isBisphenol A.
 4. The composition of claim 1, wherein the number averagemolecular weight of the epoxy-containing material is 220 to 25,000, asdetermined by multiplying the epoxy equivalent by the epoxyfunctionality.
 5. The composition of claim 4, wherein the molecularweight of the epoxy-containing material is 220 to
 4500. 6. Thecomposition of claim 1, wherein the equivalent ratio of thephosphorus-containing material to epoxy-containing material is between1.6 and 5.0:1.
 7. The composition of claim 1, wherein the curing agentis selected from the group consisting of aminoplast resins,polyisocyanates, polyacids, organometallic complexed materials,polyamines, and polyamides.
 8. The composition of claim 7, wherein thecuring agent is an aminoplast.
 9. The composition of claim 8, whereinthe aminoplast is a melamine-formaldehyde condensate.
 10. Thecomposition of claim 9, wherein the melamine-formaldehyde condensatecomprises at least 40 weight percent of imino groups.
 11. Thecomposition of claim 1, wherein the number average molecular weight ofa) is from 1000 to
 5000. 12. The composition of claim 1, wherein theweight percent of (a) is from 50 to 100, based on the total weight ofthe composition.
 13. The composition of claim 1, wherein the weightpercent of (b) is from 5 to 25, based on the total weight of theresinous binder.
 14. The composition of claim 1, further comprising oneor more corrosion resistant pigments.
 15. The composition of claim 1,wherein said composition is aqueous-based.
 16. The composition of claim1, wherein said composition is solvent-based.
 17. A process for coatinga metal substrate comprising: a) applying the composition of claim 1 tothe metal substrate, wherein the composition is at a temperature of 10°C. to 85° C.; b) curing the coating composition on the metal sheet. 18.A metal substrate coated by the process of claim
 17. 19. A coating layercombination comprising an anti-corrosion layer formed from thecomposition of claim 1, directly adjacent to a weldable coating layercomprising an electroconductive pigment and a binder.